Human-powered vehicles provide a means of self-propelled transportation that is an alternative to the relatively slow process of walking. Leg-powered vehicles and carts have long provided transportation as an alternative to motorized vehicles, and are particularly popular with children and adults who have the physical ability and motivation to use them.
Early bicycles employed foot pedals directly attached at or near the center of a drive wheel to provide power to the drive wheel and propel the vehicle. That configuration, however, was unwieldy because the drive wheel had to fit between the operator""s legs and was therefore limited in radius, and the permanently attached pedals were always in motion whenever the drive wheel was turning. Because of these limitations, this vehicle could cover only a limited amount of ground per revolution of the pedals/drive wheel, and the operator could not rest his or her legs while the vehicle was in motion. The problem of having a single rotation of the pedals cause only a single rotation of the drive wheel was eventually overcome by the development of a sprocket and drive chain system in which two sprockets could be connected by a drive chain or belt, whereby one sprocket would be attached to the pedals and a second sprocket would be attached to the drive wheel In this configuration, the size of the sprockets could be varied for different vehicles such that the ratio of drive wheel rotations per single rotation of the pedals became a function of the relative sizes (or the number of teeth on the sprocket) of each of the sprockets. Because different sizes of sprockets for the pedals and drive wheel permitted a range of speed and power, and it became possible to design and build human-powered vehicles that could operate efficiently over a wide range of surface conditions.
Along with sprocket and drive chain systems came the development of sprocket assemblies that would provide rotational torque to a drive wheel when rotated in one direction, but that would freewheel or remain stationary independently of the rotation of the drive wheel when torque was not being applied to the drive wheel. This development of such a one-way freewheeling sprocket made it possible for the human operator""s legs to remain stationary while the vehicle was in a coasting motion.
Modern bicycles employ all of these developments, and have been made even more versatile through the employment of a number of sprockets of different sizes both on the drive wheel and on the pedals. By urging or forcing the chain connecting the pedals to the drive sprocket to jump from one sized sprocket to another, it is possible for a single vehicle to exhibit a wide range of speed and power settings, simply by moving the drive chain between sprockets of different sizes at the pedals, or the drive wheel, or both. When this is done, however, the total length of the drive path along which the chain or belt must travel will become shorter or longer, depending upon the specific sprocket-to-sprocket configuration.
In order to accommodate the drive chain, which has a fixed length, throughout the variable length of the drive path, a slack take-up device must be employed. In one such device, two idler sprockets closely positioned to one another may be affixed to a partially rotatable frame which is attached to the external structure at a pivot point located somewhere on the idler frame. A portion of the drive chain between the driving wheel sprocket and the pedal sprocket is threaded around and between the two idler sprockets such that the chain passes above and around the circumference of the uppermost idler sprocket, then passes between the two sprockets, and finally passes below and around the circumference of the lower idler sprocket, leaving the device in the same general direction of travel as it had when approaching the device. A spring is used to rotate and bias the idler frame toward a configuration in which the chain traverses a maximum length path through the slack take-up device.
In general, in any device having a variable length drive path, the drive chain must be long enough to traverse the maximum anticipated length of the drive path. Obviously, when the drive path is less than the maximum length, there most be a means for taking up slack in the drive chain. Although such slack take-up devices are common on multiple-gear bicycles, the have not found significant application in other human-powered devices. Accordingly, it is an object of this invention to use a slack take-up device to compensate for a constantly varying length of drive path using a constant length drive chain in a hand powered cart. It is another object of this invention to provide a hand powered cart for vehicular transportation, exercise, and recreation.
With few exceptions, however, human powered vehicles have been designed for operation through the use of leg power to push pedals. The present invention, however, is a four-wheeled steerable cart upon which a person can sit, that can be guided by moving the front two wheels with the feet, and that is powered by a back-and-forth pumping action of the arms.
In its most basic embodiment, the cart consists of a chassis or frame upon which is mounted a seat. Two rear driving wheels are attached to an axle at the rear of the chassis, and are powered by a chain drive that provides rotational torque to a sprocket attached to the rear axle.
Two front wheels are attached to an axle at the forward end of the cart, and the direction of movement of the cart may be determined by pushing with a left or right foot upon the axle on one side or the other of the cart, thereby causing the front wheels to turn. Although other configurations may be used for steering the cart, the preferred embodiment is one in which the front axle is attached to the chassis at a single pivot point, and steering is accomplished by using the feet while the motive power for the cart is furnished by hand and arm pumping.
A power lever with handgrips on either side extends through the chassis, having a lower end in the vicinity of the drive chain which is located below the chassis, and an upper end that is approximately at shoulder level of a person seated on the cart. The power lever has a lynchpin rotatably connecting it to the chassis at or near the point that the lever extends through the chassis. The handgrips are situated such that the hands and arms are in position to provide a back and forth movement of the power lever above the chassis.
The lower extremity of the power lever has a one-way freewheeling sprocket attached to it to engage the drive chain. The drive chain forms a continuous loop, and is held in position by two idler sprockets attached to the chassis by axles, and by a slack take-up device which itself includes at least one additional idler sprockets. The drive chain also engages the drive sprocket on the rear drive wheel or axle. Power is provided to the drive chain by the one-way freewheeling sprocket attached to the lower end of the drive lever.
In operation, when the operator pulls the upper part of the power lever toward the rear of the cart, the sprocket at the lower end of the lever engages the drive chain and pulls it in a forward direction. As the chain pulls forward, it produces rotational torque upon the sprocket attached to the drive wheels, causing them to turn in the direction to move the cart forward. When upper half of the lever reaches its rearmost position, the operator will reset the lever by reversing its direction and pushing it back toward the front of the vehicle. Since the sprocket at the lower end of the lever freewheels in the reverse direction, it is now being rotated back against the drive chain, and will freewheel along the chain without causing significant backward forces to be exerted upon the drive chain. During the reset motion, the drive chain beneath the chassis will continue to be in motion, and, in the preferred embodiment, will remain in motion so long as the rear wheels are turning. In alternative embodiments, a one-way freewheeling sprocket may also be used on the rear axle, and in this configuration the car may be in motion although the drive chain may be stationary.
When the power lever has been reset, the operator may again apply a power stroke by pulling the lever toward the rear of the cart, giving the drive chain additional forward impetus, and increasing or maintaining the speed of rotation of the rear drive wheels.
The power sprocket at the lower end of the lever follows a circular arc whose radius is the distance between the sprocket and the lynchpin of the lever. The sprocket engages the drive chain at a point between two idler sprockets, and engagement of the sprocket teeth into cavities in the drive chain is ensured by maintaining sufficient tension on the drive chain to hold it in position where the power sprocket forces it to be displaced from a line which forms a tangent with each of the idler sprockets. The arcing motion of the power lever causes the drive chain to be displaced from the tangent line by varying amounts, depending upon the position of the lever at any given time. Because the motion of the power lever causes the length of the drive path between the idler sprockets to vary, the slack take-up device compensates by displacing the drive chain from its shortest path by forcing a take-up sprocket against the drive chain and maintaining that force with a spring. In this manner, the tension of the drive chain may be maintained within a reasonable range while power is applied to the rear wheels during each power stroke.